Sounds to me like you've stumbled across the 'skip to next directory' feature (short-dir+long-dir). If you go to the next track (short) and then try to fast-forward (long), you'll skip to the next directory.

I don't think so. it doesn't change directories and I don't use the FF button for selecting the song.
All I do is select a new song and FF as soon as the track starts (while it is still buffering and the playback time isn't updating).
Skipping back and fast forwarding is no problem. The issues start when I select a track that is not buffered yet.

I tried it again as you described it (load the track and FF immediately), and what happened was that there was no sound, as described in FS#9152. Pausing and resuming brought the sound back, and it was playing from the right position in the file.

no, I'm having the opposite problem: there is sound, although the wps isn't displaying any progress. I just experimented a bit with my settings and it turned out that I'm only experiencing this problem when "gather runtime data" is activated.